Illegally castrating horses is common practice in Hawke's Bay and the East Coast, an inquiry has found.

Inquiries by the Ministry for Primary Industries found that unqualified people have been carrying out this procedure not only for their own horses but as part of business enterprises.

MIP spokesman Mike Green said the inquiry had unearthed some concerning findings.

"It appears to be a practice that is well ingrained in the culture of the farming and rural community of the wider East Coast area with this service being utilised by many large station owners despite them knowing it to be illegal," Green said.

Horse castration is regarded as a significant surgical procedure and can only be carried out by a veterinarian or a veterinary undergraduate under the direct supervision of a veterinarian.

Penalties for offences under the Animal Welfare Act 1999 carry a maximum fine of $50,000 or 12 months imprisonment.

"It has certainly been a veterinarian-only procedure for more than 50 years so there are no excuses for anyone being unaware of its status.''

Green said people caught illegally castrating horses would be prosecuted - that included horse owners who allowed the illegal procedure to be done on their horses.

Veterinarians spoken to in the area said they could provide horse castration services in the more remote areas at reasonable prices provided horse owners plan and are prepared to group together for the same purpose or in conjunction with other veterinary visit needs.

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